The present invention relates to a flexible fluid containment vessel (sometimes hereinafter referred to as xe2x80x9cFFCVxe2x80x9d) for transporting and containing a large volume of fluid, particularly fluid having a density less than that of salt water, more particularly, fresh water, and the method of making the same.
The use of flexible containers for the containment and transportation of cargo, particularly fluid or liquid cargo, is well known. It is well known to use containers to transport fluids in water, particularly, salt water.
If the cargo is fluid or a fluidized solid that has a density less than salt water, there is no need to use rigid bulk barges, tankers or containment vessels. Rather, flexible containment vessels may be used and towed or pushed from one location to another. Such flexible vessels have obvious advantages over rigid vessels. Moreover, flexible vessels, if constructed appropriately, allow themselves to be rolled up or folded after the cargo has been removed and stored for a return trip.
Throughout the world there are many areas which are in critical need of fresh water. Fresh water is such a commodity that harvesting of the ice cap and icebergs is rapidly emerging as a large business. However, wherever the fresh water is obtained, economical transportation thereof to the intended destination is a concern.
For example, currently an icecap harvester intends to use tankers having 150,000 ton capacity to transport fresh water. Obviously, this involves, not only the cost in using such a transport vehicle, but the added expense of its return trip, unloaded, to pick up fresh cargo. Flexible container vessels, when emptied can be collapsed and stored on, for example, the tugboat that pulled it to the unloading point, reducing the expense in this regard.
Even with such an advantage, economy dictates that the volume being transported in the flexible container vessel be sufficient to overcome the expense of transportation. Accordingly, larger and larger flexible containers are being developed. However, technical problems with regard to such containers persist even though developments over the years have occurred. In this regard, improvements in flexible containment vessels or barges have been taught in U.S. Pat. Nos. 2,997,973; 2,998,973; 3,001,501; 3,056,373; and 3,167,103. The intended uses for flexible containment vessels is usually for transporting or storing liquids or fluidisable solids which have a specific gravity less than that of salt water.
The density of salt water as compared to the density of the liquid or fluidisable solids reflects the fact that the cargo provides buoyancy for the flexible transport bag when a partially or completely filled bag is placed and towed in salt water. This buoyancy of the cargo provides flotation for the container and facilitates the shipment of the cargo from one seaport to another.
In U.S. Pat. No. 2,997,973, there is disclosed a vessel comprising a closed tube of flexible material, such as a natural or synthetic rubber impregnated fabric, which has a streamlined nose adapted to be connected to towing means, and one or more pipes communicating with the interior of the vessel such as to permit filling and emptying of the vessel. The buoyancy is supplied by the liquid contents of the vessel and its shape depends on the degree to which it is filled. This patent goes on to suggest that the flexible transport bag can be made from a single fabric woven as a tube. It does not teach, however, how this would be accomplished with a tube of such magnitude. Apparently, such a structure would deal with the problem of seams. Seams are commonly found in commercial flexible transport bags, since the bags are typically made in a patch work manner with stitching or other means of connecting the patches of water proof material together. See e.g. U.S. Pat. No. 3,779,196. Seams are, however, known to be a source of bag failure when the bag is repeatedly subjected to high loads. Seam failure can obviously be avoided in a seamless structure. However, since a seamed structure is an alternative to a simple woven fabric and would have different advantages thereto, particularly in the fabrication thereof, it would be desirable if one could create a seamed tube that was not prone to failure at the seams.
In this regard, U.S. Pat. No. 5,360,656 entitled xe2x80x9cPress Felt and Method of Manufacturexe2x80x9d, which issued Nov. 1, 1994 and is commonly assigned, the disclosure of which is incorporated by reference herein, discloses a base fabric of a press felt that is fabricated from spirally wound fabric strips. The fabric strip of yarn material, preferably being a flat-woven fabric strip, has longitudinal threads which in the final base fabric make an angle in what would be the machine direction of the press felt.
During the manufacture of the base fabric, the fabric strip of yarn material is wound or placed spirally, preferably over at least two rolls having parallel axes. Thus, the length of fabric will be determined by the length of each spiral turn of the fabric strip of yarn material and its width determined by the number of spiral turns.
The number of spiral turns over the total width of the base fabric may vary. The adjoining portions of the longitudinal edges of the spirally-wound fabric strip are so arranged that the joints or transitions between the spiral turns can be joined in a number of ways.
An edge joint can be achieved, e.g. by sewing, melting, and welding (for instance, ultrasonic welding as set forth in U.S. Pat. No. 5,713,399 entitled xe2x80x9cUltrasonic Seaming of Abutting Strips for Paper Machine Clothingxe2x80x9d which issued Feb. 3, 1998 and is commonly assigned, the disclosure of which is incorporated herein by reference) of material or of non-woven material with melting fibers. The edge joint can also be obtained by providing the fabric strip of yarn material along its two longitudinal edges with seam loops of a known type, which can be joined by means of one or more seam threads. Such seam loops may for instance be formed directly of the weft threads, if the fabric strip is flat-woven.
While that patent relates to creating a base fabric for a press felt such technology may have application in creating a sufficiently strong tubular structure for a transport container. Moreover, with the intended use being a transport container, rather than a press fabric where a smooth transition between fabric strips is desired, this is not a particular concern and different joining methods (overlapping and sewing, bonding, stapling, etc.) are possible. Other types of joining may be apparent to one skilled in the art.
It should be noted that U.S. Pat. No. 5,902,070 entitled xe2x80x9cGeotextile Container and Method of Producing Samexe2x80x9d issued My 11, 1999 and assigned to Bradley Industrial Textiles, Inc. does disclose a helically formed container. Such a container is, however, intended to contain fill and to be stationary rather than a transport container.
It should also be noted that in the papermaking art it is known to create a fabric for use in the papermaking industry having a knitted substrate. In this regard, U.S. Pat. No. 4,948,658 issued Aug. 14, 1990 discloses a fabric which is made from a core filament comprised of a bundle of threads, whose composition may vary, enclosed by a loop thread on a knitting machine. Machine filling threads or yarns transverse the core filament and the loops of the loop threads to create the base fabric. Such a fabric may then be subject to further processing.
Also, it is well known in the papermaking art to create fabric which is impermeable to fluids, a characteristic required for an FFCV. Such fabrics involve a base substrate which may be woven of reinforcing yarns and then impregnated with a suitable resin. Examples of such structures are U.S. Pat. Nos. 6,290,818 B1 and 5,238,537.
With this in mind, the construction or make up of the fabric or tube of the FFCV, whether formed as a single piece or in segments, has to take into account various factors including flexibility, durability, tear and puncture resistance, whilst of course, as aforesaid, being impermeable to sea water. Also, in the absence of flotation devices, the buoyancy of the FFCV, particularly when being emptied and empty is also a consideration. Moreover, the construction or make up of the fabric used should be cost effective. Accordingly, depending upon the application, alternative forms of fabric construction is desirable.
It is therefore a principal object of the invention to provide for a fabric construction for an FFCV which provides for the various characteristics required.
It is a further object of the invention to provide for a fabric construction for an FFCV which may be readily varied to meet possible changing requirements for the FFCV.
A yet further object of the invention is to provide for a fabric construction which facilitates the coating thereof, or avoids or minimizes the need for the separate coating altogether.
A still further object of the invention is to provide for a fabric construction which is an alternative to a woven fabric.
Accordingly, the present invention is directed towards providing a construction of the fabric used for the tube of an FFCV. In this regard, the fabric is constructed of a number of layers of components, like that of a laminate. The layers may comprise reinforcing components, buoyancy layer or layers, layers that are impermeable or that facilitate later coating, all of which may be bound together by warp knit or stitch bonded binder yarns. The fabric may be made in strips and then assembled into a tube as set forth in U.S. Pat. No. 5,713,399 or in segments and joined together in any number of ways, including that set forth in co-pending U.S. patent application Ser. No. 10/016,640 entitled xe2x80x9cSegment Formed Flexible Fluid Containment Vesselxe2x80x9d filed contemporaneously herewith which is commonly assigned. In addition, the fabric may be manufactured as a flat roll of cloth and joined endless using either a spiral winding technique, splice or other means suitable for the purpose.